www.nature.com/scientificreports OPEN received: 31 May 2016 accepted: 27 October 2016 Published: 01 December 2016 Occurrence, temporal trends, and half-lives of perfluoroalkyl acids (PFAAs) in occupational workers in China Jianjie Fu1, Yan Gao1, Lin Cui1, Thanh Wang1, Yong Liang2,3, Guangbo Qu1, Bo Yuan1, Yawei Wang1, Aiqian Zhang1,2 & Guibin Jiang1 Paired serum and urine samples were collected from workers in a fluorochemical plant from 2008 to 2012 (n = 302) to investigate the level, temporal trends, and half-lives of PFAAs in workers of a fluorochemical plant High levels of perfluorohexane sulfonate (PFHxS), perfluorooctanoic acid (PFOA), and perfluorooctanesulfonate (PFOS) were detected in serum with median concentrations of 764, 427, and 1725 ng mL−1, respectively The half-lives of PFAAs in workers were estimated by daily clearance rates and annual decline rates of PFAAs in serum by a first-order model The geometric mean and median value for PFHxS, PFOA, and PFOS were 14.7 and 11.7, 4.1 and 4.0, 32.6 and 21.6 years, respectively, by the daily clearance rates, and they were 3.6, 1.7, and 1.9 years estimated by annual decline rates The half-lives estimated by the limited clearance route information could be considered as the upper limits for PFAAs, however, the huge difference between two estimated approaches indicated that there were other important elimination pathways of PFAAs other than renal clearance in human The half-lives estimated by annual decline rates in the present study were the shortest values ever reported, and the intrinsic half-lives might even shorter due to the high levels of ongoing exposure to PFAAs Perfluoroalkyl acids (PFAAs) are a group of highly stable man-made compounds that are used in surfactants, fluorinated polymers, and fire-resistant foams because of their unique thermal and acid resistance, as well as their hydro- and lipophobic properties1 From 1970 to 2002, approximately 96,000 tonnes of perfluorooctane sulfonyl fluoride (POSF), a perfluorooctanesulfonate (PFOS) precursor, were produced, and approximately 450–2700 tonnes of PFOS entered wastewater streams2 The 3 M Company was the main PFOS producer in history and manufactured approximately 3600 tonnes per year of POSF before 20022 PFAAs contamination was not only found around point sources, such as fluorochemical facilities3, but also detected in remote areas, such as the Tibetan Plateau4 and the Arctic5,6, due to their high historic production and continuous release The adverse effects of PFAAs on humans, such as osteoarthritis and a delay of puberty, have been proposed7,8 They were also suspected to affect adult thyroid hormone function and increase certain carcinogenic activities9,10 The 3 M Company phased out PFOS production in 2002 due to its environmental persistence and potential toxicity In 2009, the 4th meeting of the Conference of the Parties to the Stockholm Convention added PFOS, its salts and POSF into Annex B to restrict the production and usage of PFOS-related compounds, with exemptions for specific uses11 Consequently, decreasing trends in concentrations of PFOS in both environmental matrices and human body were observed12–14 Nevertheless, the production volume of PFAAs, including PFOS, has increased in China since then15, and PFAAs with shorter carbon chains, such as perfluorohexane sulfonate (PFHxS), have been produced as one of the major substitutes for PFOS Our previous study evaluated the influence of a fluorochemical manufacturing facility on the ambient environment and found three major PFAAs (PFHxS, State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China 2Institute of Environment and health, Jianghan University, Wuhan 430056, China 3School of Medicine, Jianghan University, Wuhan 430056, China Correspondence and requests for materials should be addressed to A.Z (email: aqzhang@rcees.ac.cn) or Y.W (email: ywwang@ rcees.ac.cn) Scientific Reports | 6:38039 | DOI: 10.1038/srep38039 www.nature.com/scientificreports/ perfluorooctanoic acid (PFOA), and PFOS) at higher concentrations in the surrounding environment, indicating a high exposure risk for the workers3 Moreover, PFAAs can bind to serum albumin and are prone to accumulate in the blood and liver of organisms16–18 As a result, PFAAs were frequently detected in various human serum samples The serum concentration of PFAAs ranges from single-digit ng mL−1 levels in the general population to several μg mL−1 in occupationally exposed workers19–26 However, there are great differences among the elimination rates of the individual PFAAs in humans The reported half-lives based on serum concentrations ranged from 26 days for PFBS to more than years for PFHxS and PFOS21,27,28 Moreover, the data from different sources are even controversial for the same compound Olsen et al considered the half-life of PFOS for retired fluorochemical production workers to be approximately years [95% CI, 3.9–6.9 years]21, while Zhang et al estimated that the half-life of PFOS in males and older females exceeded 10 years (average ± SE: 27 ± 3.1 years)28 Half-lives of PFAAs in humans are directly associated with the elimination pathways, while the accumulation/elimination pathways in humans are still not well known Renal elimination is one of the most critical processes in determining the total body clearance of perfluorocarboxylates (PFCAs), but other factors such as menstrual clearance and biliary excretion cannot be neglected29,30 We collected paired serum and urine samples of occupational workers in a fluorochemical plant in China from 2008 to 2012 in this study, covering important time points before and after the PFOS restriction in 2009 The body burden and temporal trends of PFOA, PFOS, and PFHxS in the workers were then investigated Furthermore, the half-lives of PFAAs in workers were estimated by both the PFAAs daily clearance and annual decline rates Methods Sample Collection. The selected fluorochemical plant (Henxin Chemical Plant) in this study is one of the largest producers of PFOS-related chemicals in China and is located in Yingcheng, Hubei province3 Perfluoroalkyl sulfonic acids (PFSAs) and perfluorotertiary amines are synthesized through an electro-chemical fluorination (ECF) process We collected paired serum and urine samples from the occupational workers in the plant for five consecutive years, and the sampling activities were carried out in Nov 2008, Nov 2009, Nov 2010, Dec 2011, and Dec 2012, respectively The Medical Research Ethics Committee, School of Medicine, Jianghan University, approved the ethics of this study, and all methods were performed in accordance with the relevant guidelines and regulations, moreover, all volunteers gave written informed consent Demographic information of the donors, including gender, age, length of service, and work assignment, was collected with a questionnaire (Table S1) The sampled population included a total of 302 occupational workers, of which there were 89 female and 213 male participants In total, 302 serum and 274 urine samples were collected The participants were told not to eat breakfast before the sampling, and morning urine samples and blood samples were collected Serum was separated from the blood by centrifugation at 1100 × g at 4 °C for 10 min and then placed on ice Serum samples were then transferred to our laboratory on the same day and stored in polypropylene containers at −20 °C until analysis Laboratory Analysis. All pre-treatment methods and instrument analysis of PFAAs in serum and urine samples are based on previous studies with minor modifications (see Supplementary Information)3,31 Based on the PFAA profiles in environmental matrices around the same plant in our previous study3, only main PFAAs, PFHxS, PFOA, and PFOS, were analyzed in the obtained serum and urine samples Instrumental analysis of the PFAAs was performed by a HPLC-ESI/MS/MS system (HPLC: Waters 2695, MS: Waters Quattro Premier XE) The limits of detection (LODs) of PFHxS, PFOA, and PFOS were 0.020, 0.063, and 0.018 ng mL−1 for serum samples and 0.008, 0.025, and 0.007 ng mL−1 for urine samples, respectively A procedural blank was performed for every batch of seven samples, and all of the blank levels were below the LODs The spiked recoveries of PFHxS, PFOA, and PFOS ranged from 95% to 110% for the serum samples and 111% to 123% for the urine samples, respectively Details of quality assurance and quality control of the chemical analysis can be found in the Supplementary Information Estimation of half-lives of PFAAs. Olsen et al.21 found linear relationship between the logarithm of serum PFAAs concentration and time, and a first order model was adopted to estimate the half-lives of PFAAs The elimination of PFAAs in humans was also described with the following equation: C (t ) = C 0e−kt (1) t 1/2 = Ln2/k (2) If we set C(t) as 1/2C0, then the half-life where k is the elimination rate constant We calculated k using two approaches in the present study In the first approach, k is defined as Cltotal/Vd, where Vd stands for the volume of distribution of PFAAs in the human body Cltotal represents the total daily PFAAs clearance in the human body; for men and women older than 50, it refers to renal clearance, while for young women, it is defined as the sum of menstrual clearance and renal clearance To keep consistency with other studies, Vd of PFOS and PFHxS were set at 230 mL kg−1, and Vd of PFOA was set at 170 mL kg−1 in this study28,32,33 In the second approach, k is defined as the average annual decline rates of PFAAs in workers who participated in this study Worker Grouping and Statistical Analysis. The PFAA body burden might relate to uncontrolled factors such as the age and gender of the donors Therefore, the donors were grouped by age, BMI (weight divided by the square of height (kg m−2)), gender, length of service, and work assignment in this plant Based on the Chinese standard of BMI, the workers were divided into three sub-groups: underweight donors with BMI lower Scientific Reports | 6:38039 | DOI: 10.1038/srep38039 www.nature.com/scientificreports/ Serum Group N PFHxS PFOA Urine PFOS N PFHxS PFOA PFOS All workers All workers 302 N > LOD 301 302 302 N > LOD 245 254 249 mean 1855 1052 5624 mean 3.9 4.3 4.4 median 764 427 1725 median 1.7 1.9 1.2 range LOD-19837 2.5–32000 50.3–118000 range LOD-77.1 LOD-53.6 LOD-81.5 274 Divide by work assignments Electrolytic department Sulfonation department Research building Fabric finishing agent department Management office 74 101 27 92 N > LOD 74 74 74 N > LOD 66 65 64 mean 1469 2337 1909 mean 2.3 6.7 1.8 median 1011 1126 1541 median 1.3 3.5 0.93 range 46.6–6759 55.9–32000 234–8501 range LOD-8.3 LOD-38.4 LOD-26.9 67 N > LOD 101 101 101 N > LOD 95 97 96 mean 3778 929 14002 mean 7.1 4.8 8.8 median 2250 603 5544 median 3.7 2.7 3.0 range 96.1–15700 4.9–4630 416–118000 range LOD-77.1 LOD-53.6 LOD-81.5 98 N > LOD 27 27 27 N > LOD 21 23 21 mean 842 404 1195 mean 1.9 1.8 1.4 median 506 142 736 median 0.97 0.92 1.1 range 3.0–3360 4.7–2920 101–7450 range LOD-7.6 LOD-15.3 LOD-6.5 25 N > LOD 8 N > LOD 8 mean 1956 606 514 mean 3.5 5.1 0.39 median 1768 114 267 median 2.4 1.5 LOD range 550–4690 51–2600 103–1890 range 0.79–7.1 1.2–22.2 LOD-1.7 N > LOD 91 92 92 N > LOD 55 61 64 mean 331 362 1144 mean 0.93 1.5 1.6 median 169 101 616 range LOD-3350 2.5–4380 50.3–7910 76 median 0.37 0.86 0.49 range LOD-8.1 LOD-9.7 LOD-12.1 Table 1. Descriptive statistics of PFAAs in serum and urine samples (all workers, divided by working location, ng mL−1) than 18, normal donors with BMI between 18 and 24, and overweight ones with BMI over 2434 For the length of service in the plant, categories, less than year, to years, and over years, were considered Considering the specific work assignments, there were five sub-groups: the workers in the sulfonation department, the fabric finishing agent department, the electrolytic process department, the research and development department, and the management office Taking age and gender into consideration, young (≤50) and old (>50) and male or female were used as classification criteria Different from the participants in the previous study, 82.3% of the workers in this study are under 50 years old 78.5% of the workers had a BMI of 18 to 24, with only 18.9% overweight, although both the mean BMI value and the cut-off point for overweight for the Chinese are much lower than those of Western people and the existing WHO classification A detailed statistical description of the factors such as the age, BMI, and gender of the groups is shown in Table S1 in the Supplementary Information The PFAA concentrations were set to LOD/2 if the concentrations in the samples were below the LOD for further statistical analysis Spearman correlation coefficients between levels were used for the correlation analysis among the levels of different PFAAs The frequency distributions of the serum PFAAs suggested log-normal distributions, which were further confirmed by the Shapiro-Wilk test Using the concentrations of PFAAs as continuous dependent variables, the models using log-transformed variates fit the data better than a model using untransformed variates Moreover, a specific general linear model was obtained by an analysis of covariance, in which the potentially confounding covariates BMI and age were set as continuous variates, while the other factors were set as categorical variates All statistical analyses were performed using SPSS statistical software (Version 17.0) Results The serum concentrations of PFHxS, PFOA, and PFOS in workers were in the ranges of electrolytic department >research building > management office >fabric finishing agent department (Table 1) The fabric finishing agent department was established in 2010, with the workers here employed after PFOS was restricted, and PFHxS or PFHxS-based products are the raw material in this department Therefore, high PFHxS exposure in this department was expected, but the workers there had a lesser and shorter exposure to PFOS Significant correlations (p